O
oopere
- Jan 1, 1970
- 0
Hi!
I am working on an EAS (Electronic Article Surveillance) design. The
objective is to design an active tag that a) beeps (screams) in the
presence of the 8.2 MHz field generated by the surveillance antennas
_and_ b) triggers the conventional alarm mechanism of the system.
To detect the RF field, we have built an LC tank where the inductor is
made of some turns on a FR4 PCB (half on each layer) spiraled around a
ferrite bar inserted through the PCB. This also triggers the basic alarm
of the system.
The question: Which is the best way to increase sensitivity of this
setup? [Sensitivity is ok by now, but we may expect that in the future
someone expects "more"]
* We can increase the number of turns and decrease line thickness ("y"
dimension is limited). This will increase inductance by a factor, but
will increase resistance due to the increased length and the decreased
cross section. Will there be net gain? Skin depth is roughly 20um at
this frequency and so does not affect on 35um copper.
* Widening the loop in the "x" direction keeping the same ferrite? This
does not make sense, since the effect of the ferrite gets more "diluted".
Additional constraints: power consumption has to be kept below 10 uA
(3V) when not beeping.
Any suggestions/pointers are welcome.
Pere
I am working on an EAS (Electronic Article Surveillance) design. The
objective is to design an active tag that a) beeps (screams) in the
presence of the 8.2 MHz field generated by the surveillance antennas
_and_ b) triggers the conventional alarm mechanism of the system.
To detect the RF field, we have built an LC tank where the inductor is
made of some turns on a FR4 PCB (half on each layer) spiraled around a
ferrite bar inserted through the PCB. This also triggers the basic alarm
of the system.
The question: Which is the best way to increase sensitivity of this
setup? [Sensitivity is ok by now, but we may expect that in the future
someone expects "more"]
* We can increase the number of turns and decrease line thickness ("y"
dimension is limited). This will increase inductance by a factor, but
will increase resistance due to the increased length and the decreased
cross section. Will there be net gain? Skin depth is roughly 20um at
this frequency and so does not affect on 35um copper.
* Widening the loop in the "x" direction keeping the same ferrite? This
does not make sense, since the effect of the ferrite gets more "diluted".
Additional constraints: power consumption has to be kept below 10 uA
(3V) when not beeping.
Any suggestions/pointers are welcome.
Pere